The objective of this project is to compare different techniques for assisting individuals with stroke-related mobility impairments using robotic ankle orthoses. Several promising assistance techniques have been developed for robotic prostheses and rehabilitation platforms. Many of these, however, have not yet been applied to powered orthoses or exoskeletons, and few have been applied at the ankle joint, despite its importance in locomotion. The efficacy of these techniques has not been tested consistently, and techniques have not been optimized for individuals with stroke nor directly compared against each other. The proposed study addresses these needs by directly comparing physiological responses to different assistance techniques provided by a versatile robotic platform. A standardized set of quantitative performance metrics are proposed, including measures of effort, preferred speed, and stability. An ankle exoskeleton emulator, previously developed by the investigators, is proposed for use due to its unique ability to express a wide range of robotic functions in a single platform. Each promising technique will first be programmed and verified in pilot tests with the emulator. Multi-dimensional parameter studies will then be performed for each assistance technique, first on subjects without neurological impairment and then on subjects with hemiparesis following stroke. Results will be used to identify optimal parameters for each approach. Finally, an across-technique comparison will be performed using optimal parameters. These tests are expected to provide a scientific foundation for the design and prescription of robotic ankle-foot orthoses that manage symptoms for millions of individuals with stroke. Results will inform improved orthosis designs and test feasibility of designs that are both effective and low-cost. Together, these results are expected to provide the evidence base to make post-stroke care more effective, less expensive, and manageable by fewer clinical practitioners, addressing the needs of our aging population and potentially leading to reduced disparities in treatment.